1. Field of the Invention
The present invention relates generally to scheduling in a mobile communication system, and more particularly, to a method and apparatus for transmitting a scheduling request signal by a User Equipment (UE) in a mobile communication system.
2. Description of the Related Art
Generally, mobile communication systems provide communication services while securing user mobility. Thanks to technology breakthroughs, the mobile communication systems have evolved to provide not only voice communication services, but also high-speed data communication services.
Standardization for Long Term Evolution (LTE) in 3rd Generation Partnership Project (3GPP) is one of the next-generation mobile communication systems. LTE is a technology that can implement high-speed packet-based communication having a maximum data rate of 100 Mbps. In order to support this high-speed communication, several methods have been discussed, such as a method of reducing the number of nodes in a communication link by simplifying the network structure, and a method of approximating wireless protocols to wireless channels, if possible.
Unlike in voice service, in data service, the amount of wireless resources allocated to one UE is determined depending on the amount of transmission data and the channel conditions. Therefore, a wireless communication system, such as the mobile communication system, manages a scheduler to allocate transmission resources taking into account the amount of transmission resources, the channel conditions, and the amount of transmission data. This is performed in the same way in LTE. A scheduler located in an evolved Node B (eNB) manages wireless transmission resources and properly allocates them to UEs.
In the wireless communication system, such as the mobile communication system, data transmission is classified into downlink transmission and uplink transmission depending on the direction of data transmission. The term ‘downlink transmission’ refers to transmission from an eNB to a UE, while the term ‘uplink transmission’ refers to transmission from a UE to an eNB.
In the case of downlink transmission, since an eNB may pinpoint the current channel conditions, the amount of allocable wireless resources, and the amount of transmission data, a scheduler in the eNB may smoothly perform scheduling based on the above information. However, in the case of uplink transmission, the scheduler in the eNB may not properly allocate wireless resources to UEs since the uplink transmission may be performed without scheduler pinpointing the current buffer status of UEs, causing difficulties in the uplink transmission.
In order to solve the difficulties in the uplink transmission, in the LTE system, a UE reports its current buffer status to an eNB using a ‘Buffer Status Report Control Element’.
The ‘Buffer Status Report Control Element’ is set to be transmitted to an eNB by a UE if certain conditions are satisfied, such as, if transmission data with a high priority is newly generated and if a predetermined timer expires.
A Buffer Status Report (BSR), occurring when new data with a high priority is generated, may be referred to as a regular BSR. In order to transmit the regular BSR to the eNB as quickly as possible, upon occurrence of a regular BSR, a UE requests transmission resources for BSR transmission by transmitting 1-bit information called Dedicated-Scheduling Request (D-SR) to the eNB. More specifically, the D-SR is used to request, from the ENB, wireless resources for transmitting a regular BSR.